Re: btrfs fi defrag -c

[Li Zefan <lizf@cn.fujitsu.com>]

Stephane Chazelas wrote:
> I don't quite understand the behavior of "btrfs fi defrag"
> 
> ~# truncate -s2G ~/a
> ~# mkfs.btrfs ~/a
>         nodesize 4096 leafsize 4096 sectorsize 4096 size 2.00GB
> ~# mount -o loop ~/a /mnt/1
> /mnt/1# cd x
> /mnt/1# df -h .
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/loop1      2.0G   64K  1.8G   1% /mnt/1
> /mnt/1# yes | head -c400M > a
> /mnt/1# df -h .
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/loop1      2.0G   64K  1.8G   1% /mnt/1
> /mnt/1# sync
> /mnt/1# df -h .
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/loop1      2.0G  402M  1.4G  23% /mnt/1
> /mnt/1# btrfs fi defrag -c a
> 
> (exit status == 20 BTW).
> 

int do_defrag(int ac, char **av)
{
	...
        return errors + 20;
}

This doesn't make sense to me.

> (20)/mnt/1# sync
> /mnt/1# df -h .
> Filesystem      Size  Used Avail Use% Mounted on
> /dev/loop1      2.0G  415M  994M  30% /mnt/1
> 
> No space gain, even lost 15M or 400M depending on how you look at it.
> 

Here's mine:

# df . -h
Filesystem            Size  Used Avail Use% Mounted on
/home/lizf/tmp/a      2.0G  409M  1.4G  23% /mnt

And I was not suprised, as there's a regression.

With this fix:

http://marc.info/?l=linux-btrfs&m=131495014823121&w=2

# df . -h
Filesystem            Size  Used Avail Use% Mounted on
/home/lizf/tmp/a      2.0G   14M  1.8G   1% /mnt